Quinacridone pigments in electrophotographic recording

ABSTRACT

AN ELECTROPHOTOGRAPHIC PLATE INCLUDING A PHOTOCONDUCTIVE LAYER COMRPISING A NOVEL QUINACRIDONE PIGMENT IN A BINDER MATERIAL, SAID QUINACRIDONE PIGMENT HAVING THE FORMULA: 2,9-BIS((2-R&#39;&#39;-PHENYL)-CO-NH-CH2-),3,10-DI(R)-QUINACRIDONE WHEREIN R=CH3, C2H5, OCH3, OC2H5 OR A HALOGEN AND WHEREIN R&#39;&#39;=COOH, COOCA/2, SO3H, OR SO3CA/2 IS DISCLOSED. METHODS OF PREPARING SAID PLATE AND OF USING SAID PLATE IN ELECTROPHOTOGRAPHIC PROCESSES ARE ALSO DISCLOSED.

United States Patent ABSTRACT OF THE DISCLOSURE An electrophotographicplate including a photoconductive layer comprising a novel quinacridonepigment in a binder material, said quinacn'done pigment having theformula:

Patented June 6, 1972 photographic plates. Vitreous selenium, however,while desirable in most aspects, suffers from serious limitations inthat its spectral response is somewhat limited to the ultra-violet, blueand green regions of the spectrum and the preparation of vitreousselenium plates requires costly and complex procedures, such as vacuumevaporation. Also, vitreous selenium layers are only metastable in thatthey are readily recrystallized into inoperative crystalline forms attemperatures only slightly in excess of those previaling in conventionalelectrophotographic copying machines. Further, selenium plates requirethe use of a separate conductive substrate layer, preferably with anadditional barrier layer deposited thereon before deposition of theselenium photoconductor. Because of these economic and commercialconsiderations, there have been N R- CHzNH o l ilm H I wherein R=CH C HOCH OC H or a halogen and wherein R=COOH, COOCa/Z, SO H, or SO Ca/2 isdisclosed. Methods of preparing said plate and of using said plate inelectrophotographic processes are also disclosed.

BACKGROUND OF THE INVENTION This invention relates, in general, toelectrophotography and, more specifically, to a binder plate usable inelectrophotography.

It is known that images may be formed and developed on the surface ofcertain photoconductive insulating materials by electrostatic means. Thebasic electrophotographic process, as taught by Carlson in US. Pat.2,297,691, involves uniformly charging a photoconductive insulatinglayer and then exposing said layer to a light-and-shadow images whichdissipates the charge on the portions of the layer which are exposed tolight. The electrostatic latent image formed on the layer corresponds tothe configuration of the light-and-shadow image. Alternatively, a latentelectrostatic image may be formed on the plate by charging said plate inimage configuration. This image is rendered visible by depositing on theimaged layer a finely divided developing material comprising a colorantcalled a toner and a toner carrier. The powdered developing materialwill normally be attracted to those portions of the layer which retain acharge, thereby forming a powder image corresponding to the latentelectrostatic image. Where the base sheet is relatively inexpensive,such as paper, the powder image may be fixed directly to the plate as byheat or solvent fusing, Alternatively, the powder image may betransferred to a sheet of receiving material, such as paper, and fixedthereon. The above general process is also described in US. Pats.2,357,809; 2,891,011; and 3,079,342.

The photoconductive insulating layer to be effective must be capable ofholding an electrostatic charge in the dark and dissipating the chargeto a conductive substrate when exposed to light. That variousphotoconductive insulating materials may be used in makingelectrophotographic plates is known. Suitable photoconductive insulatingmaterials such as anthracene, sulfur, selenium or mixtures thereof havebeen disclosed by Carlson in US. Pat. 2,297,691. These materialsgenerally have sensitivity in the blue or near ultraviolet range, andall but selenium have a further limitation of being only slightlylight-sensitive. For this reason, selenium has been the mostcommercially accepted material for use in electromany recent elfortstoward developing photoconductive insulating materials other thanselenium for use in electrophotographic plates.

It has been proposed that various two-component materials be used inphotoconductive insulating layers used in electrophotographic plates.These consist of a photoconductive insulating material in particulateform dispersed in an insulating binder. Where the particles consist of aphotoconductive material comprising inorganic crystalline compoundscontaining a metallic ion, satisfactory photographic speed and spectralresponse for use in xerographic plates are obtained. However, theseplates even when dyesensitized generally have sensitivities much lowerthan selenium. These plates are generally considered to be nonreusablesince it is necessary to use such high percentages of photoconductivepigment in order to attain adequate sensitivity that it is difiicult toobtain smooth surfaces which lend themselves to eificient toner transferand subsequent cleaning prior to reuse. An additional drawback in theuse of inorganic pigment-binder type plates is that they can be chargedonly by negative and not by positive corona discharge. This propertymakes them commercially undesirable since negative corona dischargegenerates much more ozone than positive corona discharge and isgenerally more difficult to control.

It has been further demonstrated that organic photoconductive dyes and awide variety of polycyclic compounds may be used together with suitableresin materials to form photoconductive insulating layers useful inbinder-type plates. These plates generally lack sensitivity levelsnecessary for use in conventional electrophotographic copying devices.In addition, these plates lack abrasion resistance and stability ofoperation, particularly at elevated temperatures.

In another type plate, inherently photoconductive polymers are usedfrequently in combination with sensitizing dyes or Lewis acids, to formphotoconductive insulating layers. These polymeric organicphotoconductor plates generally have the inherent disadvantages of highcost of manufacture, brittleness, and poor adhesion to supportingsubstrates. A number of these photoconductive insulating layers havethermal distortion properties which make them undesirable in anautomatic electrophotographic apparatus which often includes powerfullamps and thermal fusing devices which tend to heat theelectrophotographic plate.

Thus, there is a continuing need for improved photoconductive insulatingmaterials from which stable, sensitive, and reusable electrophotographicplates can be made.

3 SUMMARY THE INVENTION It is, therefore, an object of this invention toprovide. 7

an electrophotographic plate disadvantages.

' Another object of this invention is to provide electrophotographicplates having sensitivities which extend over substantial portions ofthe visible spectrum.

Still another object of this invention is to provide a reusableelectrophotographic plate having a high overall sensitivity and highthermal stability when compared to present commercially availablereusable plates. J

.Yet another object of this invention is to provide a photoconductiveinsulating material suitable for use in electrophotographic plates inboth single use and reusable systerns.

Yet another object of this invention is to provide a photoconductiveinsulating layer for an electrophotographic plate which is substantiallyresistant to abrasion and has a relatively high distortion temperature.

Yet another further object of this invenion is to provide anelectrophotographic plate having a wide range of useful physicalproperties.

The foregoing objects and others are accomplished in accordance withthis invention, generally speaking, by providing an electrophotographicplate having a novel photoconductive layer comprising a quinacridonepigment in a resin hinder, said quinacridone pigment having thefollowing general formula:.

devoid of the above-noted where R=CH C H OCH C H or a halogen andR=COOH, COOCa/2, SO H, or SO Ca/2. This particular class of quinacridonepigments as well as methods for their preparation are fully described incopending application, Ser. No. 772,596, filed in the US. Patent OfiiceNov. 1, 1968.

The above-described quinacridone-resin photo-conductive layer may bedeposited on any suitable supporting substrate, or may be cast as aself-supporting film. The'plate may be overcoated with any suitablematerials, if desired. The quinacridone-resin photoconductive layer maybe used in theformation of multi-layer sandwich configurations adjacenta dielectric layer, similar to that shown by Golcvinet al.', in thepublication entitled A New Electrophotographic Process, Efliected byMeans of Combined Electric Layers Doklady, Akad. Nauk SSSR vol. 129, No.5, pages 1008-1011, November-December 1959. It has been found that thepercentage of the particular class of quinacridones described abovewhich are required to produce adequate sensitivity in a plate is verylow. Because of this, the mechanical properties of thephotoconductivelayers are substantially determined by the properties ofthe binder. A widevariety of resin'binders may be used in the presentinvention, varying from soft thermoplastics to hard crosslinked enamels.Thus, the physical properties of the final photoconductive layer may bevaried over wide limits by selection of the appropriate resins to suitspecific requireinents. In this regard, these photoconductive layers aresuperior to many heretofore known binder suspensions of inorganicpigments which require a relatively high percentage of inorganic pigmentsuch that the inorganic pigment used essentially controls the physicalproperties of the final photoconductive layer. Since the percentage ofquinacridone pigment needed is relatively low, the photoconductive platemay have a very hard, very smooth surface. This eliminates many of thedisadvantages of the prior pigment-binder plates which, because of thehigh proportions of pigment, had a very rough and abrasive surface.

- 4" a i While'any of the novel class of quinacridones having theabove-described general formula may be used to prepare thephotoconductive layer of the present invention, it is preferred toemploy thoseiquinacridones wherein R is selected from the groupconsisting of CH C l-I and mixtures thereof and wherein R'=SO Ca/ 2,since these materials are highly photosensitive and produce the mostdesirable images.

Various of the above-described quinacridones may be utilized alone or incombination with other compositions in any suitable mixture, dimer,trimer, oligorner, polymer, copolyrner or mixtures thereof.

Any suitable organic binder resin may be used in combination with thenovel class of quinacridones to prepare the photoconductive layer ofthis invention. In order to be useful the resin used in the presentinvention should be more resisitive than about 10 and preferably morethan 10 ohms per centimeter under the conditions of. electrophotographicuse. Typical resins include: thermoplastics including olefin polymerssuch as polyethylene and polypropylene; polymers derived from dienessuch as polybutyldiene, polyisobutylene, and polychloroprene; vinyl andvinylidene polymers such as polystyrene, styrene-acrylonitrilecopolymers, acrylonitrile-butadiene-styrene terpolymers,polymethylmethacrylate, polyacrylates, polyacrylics, polyacrylonitiile,polyvinylacetate, polyvinyl alcohol, polyvinylchloride,polyvinylcarbazole, polyvinyl ethers, and polyvinyl ketones;fluorocarbon polymers such as polytetrafluoroethylene and polyvinylidenefluoride; heterochain thermoplastics such as polyamides, polyesters,polyurethanes, polypeptides, casein, polyglycols, polysulfides, andpolycarbonates; and cellulosic polymers such as regenerated cellulose,cellulose acetate and cellulose nitrate. Also, thermosetting resinsincluding phenolic resins; amino resins such as urea-formaldehyde resinsand melamine-formaldehyde resins; unsaturated polyester resins; epoxyresins, silicone polymers; alkyd resins and furan resins. Variouscopolymers and mixtures of the above-mentioned resins may be used whereapplicable. In addition to the above-noted resins, any other suitablematerial may be used if desired.

The quinacridone compositions of the present invention may beincorporated into the dissolved or melted binderresin by any suitablemeans such as strong shear agitation, preferably with simultaneousgrinding. Typical methods include ball milling, roller milling, sandmilling, ultrasonic agitation, high speed blending and any combinationofthese methods. Any suitable ratio of pigment to resin may be used. Ona quinacridone-dry resin Weight basis, the useful range extends fromabout 1:1 to about 1:40. Best results are obtained at, and therefore thepreferred range is, from about 1:4 to about 1:10. Optimum results areobtained when the ratio is about 1:4. While highest photosensitivity isobtained at pigment-resin ratios of 1:1 to 1:4, at the higherconcentrations of pigment dark conductivity increases. The optimumbalance between sensitivity and dark decay occurs at a ratio of about1:4. It should be noted that the proportion of photoconductor used inthe preferred'range lies substantially below that used in makingheretofore known inorganic photoconductive binder plates. In these knownplates, satisfactory electrophotographic sensitivity is attained onlywhen the pigment-resi ratio is at least 2: 1.'

1 The use in the present invention of lower pigment to resin ratiosrepresents a highly desirable advantage over the prior art since asmaller amount of the relatively expensive pigment component isrequired. Also, this permits very smooth adhesive coatings to beobtained because of the high binder content. The small proportion ofadded material has little effect on the physical properties of thebinder-resin. Thus, resins may be chosen having the desired softeningrange, smoothness, hardness, toughness, solvent resistance, orsolubility and the like with assurance that the pigment will not affectthese properties to any considerable extent.

When it is desired to coat the quinacridone-resin film on a substrate,various. supporting materials may be used. Suitable materials for thispurpose include aluminum, steel, brass, metallized or tin oxide coatedglass,

semi-conductive plastics and resins, paper and any other convenientmaterial of bulk conductivity at the time of use (ohms-cm.)- or surfaceconductivity 10 mho/square. The pigment-resin-solvent slurry (or thepigment-resin-melt) may be applied to conductive substrates by any ofthe well-known painting or coating methods, including spraying,flow-coating, knife coating, electro-coating, Mayer bar drawdown, dipcoating, reverse roll coating, etc. Spraying in an electric field may bepreferred for smoothest finish and dip coating may be preferred forconvenience in the laboratory. The setting, drying, and/or ouring stepsfor these plates are generally similar to those recommended for films ofthe particular binders as used for other painting applications. Forexample, quinacridone-epoxy plates may be cured by adding across-linking agent and stoving according to approximately about thesame schedule as other baking enamels made with the same resins andsimilar pigments for paint application. A very desirable aspect ofquinacridone compositions is that they are stable against chemicaldecomposition at the temperatures normally used for a wide variety ofbake-on enamels, and therefore, may be incorporated in very hard glossyphotoconductive coatings, having surfaces similar to automotive orkitchen appliance resin enamels.

The thickness of the quinacridone-binder films may be varied from about1 to about 100 microns, depending upon the required characteristics.Self-supporting films, for example, cannot be conveniently manufacturedin thickness thinner than about 10 microns, and are easiest to handleand use in the to 75 micron range. Coatings, on the other hand, arepreferably formed in the 5 to 30 micron range. For some compositions andpurposes, it is desirable to provide a protective overcoating. Thisovercoating should usually not exceed the thickness of a photoconductivecoating and preferably should be no more than /1 the thickness of saidcoating. Any suitable overcoating, as for example, nitrocelluloselacquer, may be employed.

6 DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples willfurther define various preferred embodiments of the present invention.Parts and percentages are by weight unless otherwise specified.

EXAMPLE I An electrophotographic plate is prepared by initially mixingabout 6 arts Pliolite SSB, a styrene-butadiene copolymer resin availablefrom Goodyear Tire and Rubber Company, about 43 parts xylene and about 1part of a quinacridone pigment having the formula H H O N u 0 C H CHzNHCg o NHCH CH3 SOsCa/Z N H Y S03Ca/2 This mixture is put into a glass jarcontaining a quantity of inch steel balls and milled on a Red 'DevilQuickie Mill (Gardner Laboratories) for about /2 hour in order to obtaina homogeneous dispersion. After milling, the dispersion is applied to asheet of 5 mil aluminum foil using a No. 36 wire draw-down rod. Thecoating, about 20 microns thick, is then forced air dried at about C.for about two hours. The plate is then charged to a positive potentialof about 650 volts by means of corona discharge, as described, forexample, in US. Pat. 2,777, 957. The charged plate is then contactexposed for 15 seconds to a film positive by means of a tungsten lamphaving a 3400 K. color temperature. The illumination level at theexposure plane is about 57 foot candles. The latent electrostatic imageformed on the plate is then developed by cascading pigmentedelectroscopic marking particles over the plate, by the processdescribed, for example, in US. Pat. 2,618,551. The powder imagedeveloped on the plate is electrostatically transferred to a receivingsheet and heat fused thereon. The image on the receiving sheet is ofvery good quality and corresponds to the contact exposed original.

EXAMPLE II An electrophotographic plate is prepared by initially mixingabout 2 parts Silicone SR-82, a methyl-phenyl silicone resin availablefrom General Electric Company, about 40 parts xylene, and about 1 partof a quinacridone pigment having the formula:

n H o N l C 2H5 CHzNH @-o NHGH N C2H5 s osrr This plate is positivelycharged to an initial potential of I about 290 volts, exposed anddeveloped. The image resulting is of satisfactory quality.

EXAMPLES III-IV COOH The plate is coated, cured, charged, exposed anddesolution in benzene, about parts cyclohexanone and veloped as in-Example '1 above, however, in-Example about 1' part of the quinacridonepigment of Example III, the plate is positively charged to a potentialof 480 II. The plates are coated, cured, charged, exposed and volts and,in Example I, the plate is charged to a negadeveloped as in Example 1above. However, here the tive potential of 835 volts. The resultingimage is of 5 plate of Example XI is charged to a positive potential ofgood quality. I about 150 volts and the plate of Example XII is chargedEXAMPLES V-VI to a negative potential of about 180 volts. Images of goodTwo electrophotographic plates are prepared by initially quahty resultmixing about 1 part of Vinylite VYNS, about parts t QQ speclficcomponents P QPQ Q have been diethyl ketone and about 1 part of aquinacridone pig- 10 desqlbed 1n the above p Telalmg the use Of a menthaving the formula: novel classof quinacridone pigments in "Ielectrophoto- 0 u a g 0 Cl- Q CHiNHC-@ @-dmiom Cl (woos/2 N y l H (I)OOOCa/Z The plate is coated, cured, charged, exposed and degraphicplates, other suitable materials, as listed above, veloped as in ExampleI above. However, here the plate may be used with similar results. Inaddition, other mateof Example V is charged to a positive potential of530 r als may be added to the qumacridor e pigment compo.- volts and theplate of Example V1 is charged to a negasitions or to the pigment-resincompositions to synergige, tive potential of 630 volts. Good imagesresult. enhance, o jB-EOCIIfZh their properties. The pig- I mentcompositions an or e pigment-resin composi- EXAMPLES VII-VH1 tions ofthisinvention maybe dyesensitized, if desired, An electrophotographicplate is prepared by initially or may be mixed or. otherwise combinedwith other photomixing about 1 part Vinylite VYNS, about 10 partsconductors, both organic and inorganic. diethyl ketone, and about 1 partof a quinacridone pig- ,Other modifications and. ramifications of thepresent merit having the formula: ,7 invention will occur to thoseskilled in the art upon a o e a t 0 OCH3- CHzNHC-@ JNHCH \N/ OCH:SOaCB/Z H SiO Calz g u t The plate is coated, cured, charged anddeveloped as in reading of the present disclosure. These are intendedExample 1 above. However, here the plate of Example to be includedwithin the scope of this invention. VI I is charged to a positivepotential of 410 volts and 40 What is claimed is: the plate of ExampleVH I is charged to a negative poten+ 1, A electrophotographic i iprocess which lial Of 605 Volts- Good images are Produced y theseprisesuniformly charging the surface of an electrophotoplates. I graphicplate comprising a self-supporting layer of an EXAMPLESelectrophotographic composition comprising a photocon- Twoelectrophotographic plates are prepared by initiallydufifivefilliflacfoidone P m in a material, Said mixing about 100 partsof a 10 percent solution of poly- I qumacridone pigment having thefollowing formula;

n g p R omnndv 0 t @-d NHCHza R N H H 7 0 vinyl carbazole i b about 5parts l 'h wherein R is selected from at least one member of the t fthnt of Exam group consisting of CH (1 1-1 OC H and a halogen and aboutIpar 0 e qumacn one plgme p l and R is selected from at least one memberof the I. These plates are coated, cured, charged, exposed and, groupconsisting of COOH COQCa/Z 803E and developed as in Example I above.However, here the plate soaca/z said layer having a thickness greaterthan about of Example IX is charged to a positive potential oi aboutlomic ns, d exposing said charged plate to a pattern 180 volts and theplate of Example X is charged to a 0f f l f g filcqomagfifitic radiationto produce an negative potential of about 215 volts. Images of goodelaclmstatlc l -i Z. An electrophotographic imaging process whichcomprises uniformly charging the surface of an electrophotographic platecomprising a support substrate having a bulk quality are produced.

EXAMPLES XI-XII conductivity greater than about 10 (ohins-centime'ter)-having superimposed thereon a photoconductive layer Electrophotographicplates are prepared by initially inixcomprising photoconductivequinacridone pigment in a ing about parts of a 10 percent polyvinylcarbazole binder, said quinacridone pigment having the formula:

0 ll H 0 N II O R CHzNHG- Q Jinncrn n it 7 i H II a o wherein R isselected from at least one member of the group consisting of CH C H OCHOC H and a halogen and wherein R is selected from at least one member ofthe group consisting of COOH, COOCa/2, SO H, and SO Ca/2, andselectively exposing said charged plate to activating electromagneticradiation to produce an electrostatic latent image.

3. The process as disclosed in claim 1 further includ ing the step ofdeveloping said latent image with electroscopic marking particles.

4. The process as disclosed in claim 2 further including the step ofdeveloping said latent image with electro scopic marking particles.

5. The process as disclosed in claim 3 wherein the imaging cycle ofcharging, exposing and developing is repeated at least once.

6. The process as disclosed in claim- 4 wherein the imaging cycle ofcharging, exposing and developing is repeated at least one time.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 1,085,680 10/1967Great Britain.

15 GEORGE F. 'LESMES, Primary Examiner J. C. COOPER HI, AssistantExaminer US. (:1. X.R.

